Sensor with integrated heater

ABSTRACT

A device includes a microelectromechanical system (MEMS) sensor die comprising a deformable membrane, a MEMS heating element, and a substrate. The MEMS heating element is integrated within a same layer and a same plane as the deformable membrane. The MEMS heating element surrounds the deformable membrane and is separated from the deformable membrane through a trench. The MEMS heating element is configured to generate heat to heat up the deformable membrane. The substrate is coupled to the deformable membrane.

RELATED APPLICATIONS

The instant application is a non-provisional patent application claimingthe benefit and priority to the U.S. Provisional Application No.62/732,325 filed on Sep. 17, 2018, which is incorporated herein byreference in its entirety. The instant application is acontinuation-in-part non-provisional patent application and claims thebenefit and priority to a U.S. application Ser. No. 16/520,228 filed onJul. 23, 2019, which is incorporated herein by reference in itsentirety. The instant application is also a continuation-in-partnon-provisional patent application and claims the benefit and priorityto a U.S. application Ser. No. 16/378,322 filed on Apr. 8, 2019, whichis incorporated herein by reference in its entirety.

BACKGROUND

Many electronic devices are used in various conditions and are exposedto different external environments. For example, sensors may come incontact with the external environment such as water that may be damagingto the sensing device in addition to causing performance degradation.Unfortunately, sensors are sensitive to these external environments,e.g., water droplets on the membrane may cause an offset resulting inperformance degradation. Moreover, electronic devices may be used indifferent temperature conditions. Unfortunately, sensor performanceshifts after it is installed on a board, e.g., soldered on a printedcircuit board (PCB), due to temperature dependent parameters, e.g.,temperature coefficient of offset (TCO). Some attempts have been made toaddress performance degradation by using calibration algorithm tocompensate for temperature effect before the sensor is installed, hencesoldered on a board. Unfortunately, calibration algorithm used beforesoldering the sensor does not address or compensate for temperaturecoefficient offset resulting after soldering the sensor.

SUMMARY

Accordingly, a need has arisen to calibrate the sensor after it issoldered on a board in order to address temperature coefficient offset.Furthermore, a need has arisen to address and remove liquid from thesensor environment when liquid is detected.

In some embodiments, a device includes a microelectromechanical system(MEMS) sensor die comprising a deformable membrane, a MEMS heatingelement, and a substrate. The MEMS heating element is integrated withina same layer and a same plane as the deformable membrane. The MEMSheating element surrounds the deformable membrane and is separated fromthe deformable membrane through a trench. The MEMS heating element isconfigured to generate heat to heat up the deformable membrane. Thesubstrate is coupled to the deformable membrane.

In some embodiments, the trench is within a passivation layer. It isappreciated that a material within the trench may be selected from agroup consisting of Silicon Nitride and Silicon Oxide.

In some embodiments, the device includes a second trench. The trench isdisposed between the MEMS heating element and the membrane and thesecond trench is disposed on an outer periphery of the MEMS heatingelement configured to electrically isolate the MEMS heating element fromthe peripheral layer. It is appreciated that the second trench isdisposed between a peripheral layer and the MEMS heating element.

In some embodiments, a periphery of the deformable membrane is disposedon an oxide layer. The deformable membrane, the oxide layer, and thesubstrate form a cavity, and the substrate includes an electrode that isformed on a top surface of the substrate that faces the deformablemembrane within the cavity. According to some embodiments, the MEMSheating element is disposed on the oxide layer.

It is appreciated that in some embodiments the MEMS heating element isconfigured to generate heat for calibration responsive to temperaturecoefficient of offset (TCO) after the MEMS sensor die is soldered on aboard. In an alternative embodiment, the MEMS heating element isconfigured to generate heat responsive to detecting presence of liquidon the deformable membrane.

In some embodiments, a device includes a MEMS sensor die comprising adeformable membrane, a MEMS heating element, and a substrate. The MEMSheating element is integrated within a same layer and a same plane asthe deformable membrane. The MEMS heating element is disposed on aperiphery of the deformable membrane and is configured to generate heatto heat up the deformable membrane. The substrate is coupled to thedeformable membrane. It is appreciated that the deformable membrane maybe formed from a poly/single crystalline silicon layer.

In some embodiments, the device further includes another MEMS heatingelement integrated within the same layer and the same plane as thedeformable membrane. The MEMS heating element and the another MEMSheating element are separated from one another. The another MEMS heatingelement is disposed on the periphery of the deformable membrane and isconfigured to generate heat to heat up the deformable membrane.

In some embodiments, the MEMS heating element has a gap therein. TheMEMS heating element surrounds the membrane without fully encompassingthe deformable membrane.

It is appreciated that in some embodiments, the device further includesa trench disposed in between the MEMS heating element and the deformablemembrane. In some embodiments, the trench comprises a passivation layer.In some embodiments, the device further includes another trench that isdisposed on an outer periphery of the MEMS heating element configured toelectrically isolate the MEMS heating element from the peripheral layer.The another trench may be disposed between a peripheral layer and theMEMS heating element.

It is appreciated that in some embodiments a device further includes atrench disposed in between the MEMS heating element and the deformablemembrane. The trench comprises a material within the trench is selectedfrom a group consisting of Silicon Nitride and Silicon Oxide.

In some embodiments, a periphery of the deformable membrane is disposedon an oxide layer. The deformable membrane, the oxide layer, and thesubstrate form a cavity. The substrate includes an electrode that isformed on a top surface of the substrate that faces the deformablemembrane within the cavity. The MEMS heating element is disposed on theoxide layer.

The MEMS heating element may be configured to generate heat forcalibration responsive to TCO after the MEMS sensor die is soldered on aboard. It is appreciated that in some embodiments, the MEMS heatingelement may be configured to generate heat responsive to detectingpresence of liquid on the deformable membrane.

In some embodiments a device includes a sensor die comprising adeformable membrane, a substrate coupled to the deformable membrane, anda heating element disposed on a periphery of the deformable membrane andwithin the sensor die. The heating element is configured to heat thedeformable membrane.

In some embodiments, the heating element has a gap therein. It isappreciated that the heating element surrounds the membrane withoutfully encompassing the deformable membrane, in some embodiments.

In some embodiments, a device further includes a trench disposed inbetween the heating element and the deformable membrane. The trenchcomprises a passivation layer.

In some embodiments, the device further includes another trench that isdisposed on an outer periphery of the heating element configured toelectrically isolate the heating element from the peripheral layer. Itis appreciated that the another trench may be disposed between aperipheral layer and the heating element.

In some embodiments, a periphery of the deformable membrane is disposedon an oxide layer. It is appreciated that the deformable membrane, theoxide layer, and the substrate form a cavity. The substrate includes anelectrode that is formed on a top surface of the substrate that facesthe deformable membrane within the cavity. It is appreciated that theheating element may be disposed within a same layer as the oxide layer,e.g., on or within the oxide layer.

It is appreciated that the heating element is configured to generateheat for calibration responsive to TCO after the sensor die is solderedon a board. In some embodiments, the heating element is configured togenerate heat responsive to detecting presence of liquid on thedeformable membrane.

These and other features and aspects of the concepts described hereinmay be better understood with reference to the following drawings,description, and appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1B show a top view and a cross-sectional view of a sensor withheater integrated therein in accordance with some embodiments.

FIG. 2 shows a sensor device with a heater integrated therein configuredto heat to evaporate water droplets on its deformable membrane inaccordance with some embodiments.

FIG. 3 shows another sensor device with a heater integrated therein inaccordance with some embodiments.

FIG. 4 shows yet another sensor device with a heater integrated thereinin accordance with some embodiments.

FIG. 5 shows an alternative sensor device with a heater integratedtherein in accordance with some embodiments.

FIGS. 6A-6B show top views of a sensor with different heaterconfiguration integrated therein in accordance with some embodiments.

DETAILED DESCRIPTION

Before various embodiments are described in greater detail, it should beunderstood by persons having ordinary skill in the art that theembodiments are not limiting, as elements in such embodiments may vary.It should likewise be understood that a particular embodiment describedand/or illustrated herein has elements which may be readily separatedfrom the particular embodiment and optionally combined with any ofseveral other embodiments or substituted for elements in any of severalother embodiments described herein.

It should also be understood by persons having ordinary skill in the artthat the terminology used herein is for the purpose of describing thecertain concepts, and the terminology is not intended to be limiting.Unless indicated otherwise, ordinal numbers (e.g., first, second, third,etc.) are used to distinguish or identify different elements or steps ina group of elements or steps, and do not supply a serial or numericallimitation on the elements or steps of the embodiments thereof. Forexample, “first,” “second,” and “third” elements or steps need notnecessarily appear in that order, and the embodiments thereof need notnecessarily be limited to three elements or steps. It should also beunderstood that, unless indicated otherwise, any labels such as “left,”“right,” “front,” “back,” “top,” “middle,” “bottom,” “forward,”“reverse,” “clockwise,” “counter clockwise,” “up,” “down,” or othersimilar terms such as “upper,” “lower,” “above,” “below,” “vertical,”“horizontal,” “proximal,” “distal,” “periphery”, “outer”, and the likeare used for convenience and are not intended to imply, for example, anyparticular fixed location, orientation, or direction. Instead, suchlabels are used to reflect, for example, relative location, orientation,or directions. It should also be understood that the singular forms of“a,” “an,” and “the” include plural references unless the contextclearly dictates otherwise.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by persons of ordinaryskill in the art to which the embodiments pertain.

Many electronic devices are used in various conditions and are exposedto different external environments. For example, sensors may come incontact with the external environment such as water that may be damagingto the sensing device in addition to causing performance degradation.Unfortunately, sensors are sensitive to these external environments,e.g., water droplets on the membrane may cause an offset resulting inperformance degradation. Moreover, electronic devices may be used indifferent temperature conditions. Unfortunately, sensor performanceshifts after it is installed on a board, e.g., soldered, due totemperature dependent parameters, e.g., temperature coefficient ofoffset (TCO). Some attempts have been made to address performancedegradation by using calibration algorithm to compensate for temperatureeffect before the sensor is installed, hence soldered on a board.Unfortunately, calibration algorithm used before soldering the sensordoes not address or compensate for temperature coefficient offsetresulting after soldering the sensor.

Accordingly, a need has arisen to calibrate the sensor after it issoldered on a board in order to address temperature coefficient offset.Furthermore, a need has arisen to address and remove liquid from thesensor environment when liquid is detected.

Referring now to FIGS. 1A-1B, a top view and a cross-sectional view of asensor with heater integrated therein in accordance with someembodiments are shown. Referring specifically to FIG. 1A, a deformablemembrane 110 surrounded by a heater element 120 is shown. It isappreciated that the sensor device may be a microelectromechanicalsystem (MEMS) sensor die. The MEMS sensor die comprises a deformablemembrane 110, substrate 140, oxide 150, electrode 170, a heater element120, trenches 112-113, and a peripheral layer 180, e.g., polysiliconlayer. The heater 120 element may be generally referred to as a heater,MEMS heater, etc., throughout the instant application. The heater 120may be integrated within a same layer and a same plane as the deformablemembrane 110 (this is better illustrated in FIG. 1B). It is appreciatedthat in some embodiments, the heater 120 may be separated from thedeformable membrane 110 and from the peripheral layer 180 via trenches112-113. In some embodiments, substrate 140 may comprise silicon. Inother embodiment, substrate could be a CMOS substrate with electricalcircuits. It is appreciated that the inner trench 112 (i.e. at the innerperiphery) electrically isolates the heater 120 from the deformablemembrane 110 while the outer trench 113 (i.e. at the outer periphery)separates the heater 120 and electrically isolates it from theperipheral layer 180. It is appreciated that the heater 120 may composeof a silicon ring that surrounds the deformable membrane 110. Thedeformable membrane 110 may be formed from a polysilicon layer.

The heater 120 may be coupled to the heater pad 122 in order to powerthe heater 120. It is appreciated that the heater 120 is configured togenerate heat in order to heat the deformable membrane 110. In someembodiments, the heater 120 generates heat for calibration responsive toTCO after the MEMS sensor die is soldered on a board. For example, whenan offset is detected the heater 120 may increase the temperature by 10°C. increments in order to calibrate. It is appreciated that increasingthe temperature by 10° C. is for illustrative purposes and should not beconstrued as limiting the embodiments. For example, the heater 120 maybe configured to heat up in 5° C. increments, as an example. It isfurther appreciated that the calibration may occur responsive to atrigger, e.g., user request, meeting a certain threshold, etc. Forexample, the trigger may be a signal generated responsive to detectingpresence of liquid on the deformable membrane, responsive to measuringan offset, responsive to measuring a temperature difference between theMEMS device and the substrate that is greater than a threshold amount,etc.

In some embodiments, the heater 120 element may be configured togenerate heat responsive to detecting presence of liquid, e.g., waterdroplets, on the deformable membrane. For example, in some embodiments,the heater 120 may heat up to 100° C. or slightly higher than that inorder to heat up the deformable membrane 110 and cause water droplets onthe deformable membrane 110 to evaporate. As such, any offset associatedwith presence of water droplets can be addressed by evaporating it. Itis further appreciated that presence of water is for illustrativepurposes and should not be construed as limiting the scope of theembodiments. For example, the embodiments are equally applicable toother forms of fluids, e.g., oil. It is appreciated that embodimentsdescribed herein can be applied to sensor devices that address liquidintrusion, as described in the U.S. patent application Ser. No.16/520,228 and a U.S. application Ser. No. 16/378,322, both of which areclaimed the benefit and priority to and are incorporated herein byreference in their entirety.

Referring specifically to FIG. 1B, a side view of a device with a heaterintegrated therein in accordance with some embodiments is shown. It isappreciated that the deformable membrane 110, the heater 120, and thetrenches 112-113 are similar to that described in FIG. 1A. In thisembodiment, the heater 120 is within the same layer and plane as thedeformable membrane 110. In this embodiment, the heater 120 is withinthe same layer and plane as the peripheral layer 180. According to someembodiments, the heater 120 and the peripheral layer 180 are depositedon an oxide layer 150. In some embodiment, heater 120 and deformablemembrane 110 comprise of polysilicon. Furthermore, it is appreciatedthat the periphery of the deformable membrane 110 may be coupled to theupper surface of the oxide 150 layer. It is appreciated that the oxidelayer 150 may be formed over a substrate 140, e.g., a silicon substrate.Accordingly, the deformable membrane 110 the oxide layer 150 and thesubstrate 140 form a cavity 160. The deformable membrane 110 may deflectresponsive to a stimuli, e.g., pressure. In some embodiments, anelectrode 170 may be formed over the upper surface of the substrate 140that is disposed at the bottom of the cavity 160 facing the deformablemembrane 110. The deformable membrane 110 may also include an electrode(not shown) for thereon or integrated therein. The electrode on thedeformable membrane and electrode 170 for a capacitor. As such,deflection of the deformable membrane 110 changes the charges on theelectrodes of the capacitor.

It is appreciated that in some embodiments the trenches 112 are within apassivation layer. It is appreciated that in some embodiments, thetrenches 112 may be deposited with certain material such as SiliconNitride, Silicon Oxide, etc. As illustrated, an inner trench and anouter trench are used. For example, the inner periphery trench is atrench disposed between deformable membrane 110 and the heater 120 whilethe outer periphery trench is a trench disposed between the heater 120and the peripheral layer 180.

It is appreciated that the heater 120 is designed within a same layer asthe surrounding sensor membrane, e.g., single crystalline silicon.Accordingly, a need to use any adjacent metal structure layers iseliminated, thereby reducing metal stress effect. Moreover, using theheater 120 enables the device to calibrate after the sensor is solderedon board or throughout its lifetime. It is also appreciated that use ofthe heater 120, as described, is a liquid ejection mechanism, e.g., byevaporating liquid such as water or oil. Moreover, it is appreciatedthat the heater 120, as described, surrounds the deformable membrane110, thus creates temperature uniformity for the deformable membrane110. However, it is appreciated that in some embodiments, the heater 120may include a plurality of heaters that is separated by a gap therein orthe heater 120 may not completely surround and encompass the deformablemembrane 110. Thus, the heater 120 surrounding and encompassing thedeformable membrane 110 is for illustrative purposes only and should notbe construed as limiting the scope of the embodiments. It is appreciatedthat other structural configurations are shown in subsequent figures. Itis also appreciated that in some embodiments another heater (not shown)may be used to heat the substrate 140 while the heater 120 may be usedto heat the sensor 101 (i.e. MEMS device such as a pressure sensor) suchthat the heater 120 is used to selectively fine tune the temperature ofthe MEMS device by heating the deformable membrane 110 and to reduce thetemperature difference between the substrate 140 and the MEMS device101. It is appreciated that the calibration may occur responsive to atrigger, e.g., user request, meeting a certain threshold, etc. Forexample, the trigger may be a signal generated responsive to detectingpresence of liquid on the deformable membrane, responsive to measuringan offset, responsive to measuring a temperature difference between theMEMS device and the substrate that is greater than a threshold amount,etc.

FIG. 2 shows a sensor device with a heater integrated therein configuredto heat to evaporate water droplets on its deformable membrane inaccordance with some embodiments. FIG. 2 is substantially similar tothat of FIGS. 1A-1B. In this embodiment, a water droplet 190 is formedover the deformable membrane 110, thereby creating an offset and causingperformance issues. It is appreciated that presence of water droplet 190may have been detected by the device. As such, the heater 120 elementmay start heating up to 100° C. or slightly above 100° C. to heat thedeformable membrane 110. As such, the water droplet 190 is evaporated inresponse thereto, thereby addressing any offsets created resulting fromthe water droplet 190.

Referring now to FIG. 3, another sensor device with a heater integratedtherein in accordance with some embodiments is shown. FIG. 3 issubstantially similar to those described in FIGS. 1A-2. However, in thisembodiment, the heater 120 is integrated within the oxide layer 150instead of being within the same layer and plane as the deformablemembrane 110 or the peripheral layer 180. In other words, the heater 120is integrated within the oxide layer 150 and below the peripheral layer180 and the deformable membrane 110.

Referring now to FIG. 4, yet another sensor device with a heaterintegrated therein in accordance with some embodiments is shown. FIG. 4is similar to that of FIG. 3 except that in this embodiment, the lowersurface of the heater 120 is in contact with the upper surface of thesubstrate 140.

Referring now to FIG. 5, an alternative sensor device with a heaterintegrated therein in accordance with some embodiments is shown. FIG. 5is similar that of FIG. 4 except that at least one side of the heater120 is exposed to the cavity 160. As such, the heater 120 heating upalso heats up the cavity 160 and therefore the deformable membrane 110.

Referring now to FIG. 6A, a top view of a sensor with different heaterconfiguration integrated therein in accordance with some embodiments isshown. In this embodiment, four heaters are used, e.g., heaters 620. Theheaters 620 are separated from one another through a gap or trench 612.The deformable membrane 110 is surrounded by an inner crystallinesilicon layer 630 a. It is appreciated that use of crystalline siliconlayer is for illustrative purposes and should not be construed aslimiting the embodiments. For example, a polysilicon layer may be used.The trench 612 separates the heaters 620 from the crystalline siliconlayer 630 a and the deformable membrane 110. It is appreciated that thetrench 612 also separates the heaters 620 from the outer crystallinesilicon layer 630 b in order to provide electrical isolation with theperipheral layer (not shown here).

Referring now to FIG. 6B, a top view of a sensor with different heaterconfiguration integrated therein in accordance with some embodiments isshown. In this embodiment, a single heater 620 is used where itsubstantially surrounds the deformable membrane 110 without completelyenclosing it. As such, the two ends of the heater 620 are separated fromone another using a gap or a trench. The trench 616 separates the heater620 from the inner crystalline silicon layer 630 a whereas trench 618separates the heater 620 from the outer crystalline silicon layer 630 b.The trenches 612, 616 and/or 618 may be formed on a passivation layerand may include material such as Silicon Nitride, Silicon Oxide, etc.

FIGS. 6A and 6B are illustrated to show that the heater may have anyshape or form. As such, a particular shape or the number of heaters usedare for illustrative purposes only and should not be construed aslimiting the embodiments. Accordingly, the sensor can calibrate after itis soldered on a board in order to address temperature coefficientoffset. Furthermore, liquids can be removed from the sensor environmentwhen liquid is detected by heating up the heater element and thereby thedeformable membrane, thereby addressing any offset resulting frompresence of the liquids. It is appreciated that the calibration mayoccur responsive to a trigger, e.g., user request, meeting a certainthreshold, etc. For example, the trigger may be a signal generatedresponsive to detecting presence of liquid on the deformable membrane,responsive to measuring an offset, responsive to measuring a temperaturedifference between the MEMS device and the substrate that is greaterthan a threshold amount, etc.

While the embodiments have been described and/or illustrated by means ofparticular examples, and while these embodiments and/or examples havebeen described in considerable detail, it is not the intention of theApplicants to restrict or in any way limit the scope of the embodimentsto such detail. Additional adaptations and/or modifications of theembodiments may readily appear to persons having ordinary skill in theart to which the embodiments pertain, and, in its broader aspects, theembodiments may encompass these adaptations and/or modifications.Accordingly, departures may be made from the foregoing embodimentsand/or examples without departing from the scope of the conceptsdescribed herein. The implementations described above and otherimplementations are within the scope of the following claims.

What is claimed is:
 1. A device comprising: a microelectromechanicalsystem (MEMS) sensor die comprising: a deformable membrane; a MEMSheating element integrated within a same layer and a same plane as thedeformable membrane; wherein the MEMS heating element is disposed on theouter periphery of the deformable membrane; wherein the MEMS heatingelement is electrically isolated from the deformable membrane by atrench; wherein the MEMS heating element is configured to generate heatto heat up the deformable membrane.
 2. The device of claim 1, whereinthe trench is within a silicon layer.
 3. The device of claim 1, whereina material within the trench is selected from a group consisting ofSilicon Nitride and Silicon Oxide.
 4. The device of claim 1 furthercomprising another trench, wherein the another trench is positioned onan outer periphery of the MEMS heating element configured toelectrically isolate the MEMS heating element from a peripheral layer.5. The device of claim 1, wherein a periphery of the deformable membraneis positioned on an oxide layer, and wherein the deformable membrane,the oxide layer, and the substrate form a cavity, and wherein thesubstrate includes an electrode that is formed on a top surface of thesubstrate that faces the deformable membrane within the cavity.
 6. Thedevice of claim 5, wherein the MEMS heating element is disposed on theoxide layer.
 7. The device of claim 1, wherein the MEMS heating elementis configured to generate heat for calibration responsive to temperaturecoefficient of offset (TCO).
 8. The device of claim 7, wherein thecalibration is performed in response to a trigger.
 9. The device ofclaim 1, wherein the MEMS heating element is configured to generate heatresponsive to detecting presence of liquid on the deformable membrane.10. A device comprising a microelectromechanical system (MEMS) sensordie comprising: a deformable membrane; a MEMS heating element integratedwithin a same layer and a same plane as the deformable membrane, whereinthe MEMS heating element is disposed on a periphery of the deformablemembrane and is configured to generate thermal energy to heat up thedeformable membrane; and a substrate.
 11. The device of claim 10 furthercomprising another MEMS heating element integrated within the same layerand the same plane as the deformable membrane, wherein the MEMS heatingelement and the another MEMS heating element are separated from oneanother, and wherein the another MEMS heating element is positioned onthe periphery of the deformable membrane and is configured to generatethermal energy to heat up the deformable membrane.
 12. The device ofclaim 10, wherein the MEMS heating element has a gap therein, whereinthe MEMS heating element surrounds the membrane without fullyencompassing the deformable membrane.
 13. The device of claim 10 furthercomprising a trench disposed in between the MEMS heating element and thedeformable membrane, and wherein the trench comprises a material withinthe trench is selected from a group consisting of Silicon Nitride andSilicon Oxide.
 14. The device of claim 10, wherein a periphery of thedeformable membrane is disposed on an oxide layer, and wherein thedeformable membrane, the oxide layer, and the substrate form a cavity,and wherein the substrate includes an electrode that is formed on a topsurface of the substrate that faces the deformable membrane within thecavity, and wherein the MEMS heating element is disposed on the oxidelayer.
 15. The device of claim 10, wherein the deformable membrane isformed from a peripheral layer.
 16. The device of claim 10, wherein theMEMS heating element is configured to generate heat for calibrationresponsive to temperature coefficient of offset (TCO) after the MEMSsensor die is soldered on a board.
 17. The device of claim 10, whereinthe MEMS heating element is configured to generate heat responsive todetecting presence of liquid on the deformable membrane.
 18. A sensordie comprising: a deformable membrane; a substrate; and a heatingelement disposed on a periphery of the deformable membrane, and whereinthe heating element is configured to heat the deformable membrane. 19.The sensor die of claim 18, wherein the heating element is disposedwithin an oxide layer.
 20. The sensor die of claim 18, wherein aperiphery of the deformable membrane is disposed on an oxide layer, andwherein the deformable membrane, the oxide layer, and the substrate forma cavity, and wherein the substrate includes an electrode that is formedon a top surface of the substrate that faces the deformable membranewithin the cavity, and wherein the heating element is disposed withinthe oxide layer.